22 GEOLOGY OF ILLINOIS. 



. The Buff Limestone. Between the Blue limestone and 

 the St. Peter's, or upper sandstone, there exists a thin for- 

 mation known as the Buff limestone, not recogni/ed at all 

 by the early Western geologists. The learned PERCIVAL 

 mentions buff-colored strata or bands, noticed by him in 

 his examinations of the Wisconsin lead regions. WHITNEY, 

 in his geology of the lead regions of Wisconsin, gives it a 

 thickness at Beloit of some forty-five feet, and at Winslow 

 a thickness of some thirty feet. Following the section of 

 WHITNEY at Beloit, I have called the similar section at 

 Kockton the Buff limestone, and found its thickness to be 

 some forty feet. But most of the sections and outcrops 

 through this part of the State are thinner, averaging per- 

 haps not over eighteen or twenty feet in thickness. This 

 limestone is a heavy-bedded, dull colored rock, giving a 

 dull, heavy thud or sound when struck by the hammer, as 

 if the sound came from striking a lump of frozen earth. 

 Some of the shaly divisions are very fossiliferous, being 

 covered with shells and fragments of shells. In some quar- 

 ries near Dixon, the strata are massive and solid, and give 

 out almost a metallic ring, when struck by the hammer. 

 In a few instances, as on Pine creek, where the Buff and 

 St. Peter's sandstone meet, the line of junction between the 

 two is hard to determine. Hand specimens obtained there 

 seemed to be a mixture of both sandstone and limestone. 

 At other quarries some greenish shales and clays inter- 

 vened between the two rocks. Some of the layers are a 

 compact, semi-crystaline magnesian limestone, one or two 

 feet in thickness. 



The upper portions of this formation or division are 

 thin-bedded, and of a dull ashy-buff color. They break up 

 into small fragments near the top, and greatly resemble 

 some of the outcrops of the Blue limestone above. 



The rock forms a good building material, but the super- 

 ficial area underlaid by it is quite limited in this part of 

 the State. It outcrops around the St. Peter's sandstone in 



